The cooling system has two functions. The first and most important is to keep the engine at a manageable temperature. the cooling is used to cool engine as well as protect engine and gaskets from rust, corrosion and rot. the coolant temperature is maintained be a thermostat that keeps the coolant in the radiator long enough to cool it. The portion of coolant in the engine stays in the engine, cooling the engine till it's temperature is no longer manageable and then the thermostat releases it back into the radiator for cooling off. The second function is to provide heat to the vehicles cabin (passenger compartment) throw a heater core that transfers the coolant temperature to a heater core and air is blown across the cores heat fins to product warm air that is blown throw ducts and out to the cabin.
Cooling system operation and integrity is one of the engines critical parts, without it a engine can not run for a longer time or last for long.